The present invention relates to a method of rapid-setting a formed body to improve the surface integrity and handling of such body during the pre-firing process.
It is becoming increasingly common to process or form highly loaded plastically deformable mixtures into complex structures such as a honeycomb configuration formed by extrusion. Immediately upon forming, the resulting structure is generally soft and fragile, and easily damaged or distorted, making the handling and processing of such structures very difficult.
There is need for a more effective rapid-setting process during the pre-firing stage to reduce the amount of waste and increase the productivity of such operations. In the conventional method, cellular monoliths for example, are heated in air with various forms of energy such as thermal, dielectric, IR or induction. The conventional mechanism involves the diffusion and vaporization of batch water at or above 100.degree. C. to achieve solidification or stiffening through de-water and binder gelation. Large amounts of energy (heat) is required to vaporize water at this temperature particularly through air, a poor heat transfer medium. As a result, relatively long periods of time are required to achieve solidification of such monoliths during the manufacturing process.
Various methods have been proposed for reducing the solidification time including the application of intense heat from an infra-red, induction or dielectric source, or the use of certain chemical reactions such as an alginate/Ca ion system. The former is inefficient and is a relatively slow process due to the use of a lot of energy for the heating of sometimes, very poor heat conductors such as Celcor.RTM.. The latter process presents a difficult problem as it attempts to remove the residual Ca, often by a post wash operation which results in a resoftening of the product. Also, the residual Ca will tend to alter the batch composition.
There is nothing in the background art suggesting the use of relatively clean and energy efficient liquid compounds for the rapid-setting of formed structures. In particular, there has been no teaching or suggestion to use such liquids to rapidly stiffen cellular structures formed from thermally gelable organic binders such as Methocel.RTM., a methyl cellulose containing binder.